In recent work, researchers have supplemented traditional IS adoption models with new constructs that capture users’ relational, social, and emotional beliefs. These beliefs have given rise to questions regarding their antecedents and the nature of the user-artifact relationship. This paper sheds light on these questions by asserting that users perceive and respond to information technology (IT) artifacts as social partners and form perceptions about their social characteristics. Subsequently, users’ perceptions of the similarity of these characteristics to their own affect evaluations of these artifacts. Within the context of online shopping and using an automated shopping assistant, our paper draws upon social psychology and human-computer interaction research in developing hypotheses regarding the effects of perceived personality similarity (PPS) and perceived decision process similarity (PDPS) on a number of beliefs (enjoyment, social presence, trust, ease of use, and usefulness). The results indicate that PDPS acts as an antecedent to these beliefs, while the effects of PPS are largely mediated by PDPS. Furthermore, the results reveal that the effects of perceived similarity, in general, exceed those of the effects of the individual assessments of the user’s and the assistant’s personalities and decision processes. These results have important implications for IS design. They highlight the importance of designing artifacts that can be matched to users’ characteristics. They also underscore the importance of considering similarity perceptions rather than solely focusing on perceptions of the IT artifact’s characteristics; a common approach in IS adoption research.